1. Field of the invention
The present invention relates in general to refrigerators. More particularly, the invention relates to refrigerators having a quick cooling system.
2. Description of the prior art
It is known to provide a refrigerator with a quick cooling system which can freeze foods stored in a freezer thereof quickly by operating a compressor thereof for a predetermined period of time regardless of a refrigerator temperature. This type of refrigerator has a quick cooling starting switch which can be actuated to start the quick cooling operation. When the starting switch is actuated, the quick cooling operation is immediately started and continues for the predetermined time period, e.g. for ninety minutes.
It is also known to automatically begin a quick cooling operation. An example of such a refrigerator is disclosed in Japanese Patent Laid-Open Publication No. 58-179785 filed Apr. 16, 1982 in the name of Kosuke Atarashiya. According to Japanese Patent Laid-Open Publication No. 58-179785, the refrigerator has a food detecting plate on which foods to be frozen are placed in a freezer thereof. The food detecting plate includes four resistors which are part of a Wheatstone bridge circuit, which is balanced when nothing is put on the food plate. When food to be frozen is put on the food detecting plate, the resistance of one of the resistors is changed by the heat of the food. Therefore, the Wheatstone bridge becomes unbalanced and an output voltage is generated therefrom. This output voltage is detected and used to start the operation of the quick cooling system.
Recently there has been a great demand for refrigerators having a quick cooling operation that is completed at a desired time, enabling the user to remove cooled food from the refrigerator a predetermined amount of time after the food has been placed therein. For example, food to be cooled can be placed in a freezer or a refrigerating compartment of the refrigerator in the morning and can be removed frozen or cooled to a low temperature in the evening.
However, in known refrigerator arrangements, defrosting operations can interfere with quick cooling. Since quick cooling operation is started immediately after the starting switch is activated, or in the case of automatic quick cooling, immediately after food is placed on the food detecting plate, there is a possibility that a defrosting operation may be carried out before the food frozen or cooled by the quick cooling operation is removed from the refrigerator. When this occurs, food that should be continuously cooled by a quick cooling operation may actually be heated during a defrosting operation. In order to avoid this improper situation, in the refrigerator whose quick cooling operation is started manually, the quick cooling operation starting switch must be actuated at an appropriate time so that the quick cooling operation will be completed at the desired ending time of quick cooling. Food can then be removed before any defrosting operation is begun. This type of operation is inconvenient because the refrigerator user has to decide the proper time by reckoning backward and must be home to initiate quick cooling.